1. Field of the Invention
This invention relates to a method for heteroepitaxial growth of a two-dimensional material on a three-dimensional material, and more particularly the invention relates to a method of heteroepitaxial growth a two-dimensional single-crystal superthin film material, such as a layered superconductive substance, on a normal surface of a three-dimensional material such as semiconducting material. The method of the invention is very important in that it facilitates production of new electronic devices using key elements of heterojunction, such as quantum well type semiconducting laser, high-electron-mobility type transistors, heterobipolar transistors, resonant tunnel elements, superlattice elements, Josephson junction devices, and the like.
2. Description of the Prior Art
The art of forming a single-crystal superthin film of one material on the surface of a single crystal of another material is one of very important techniques, which techniques facilitate realization of new electronic devices using key elements of heterostructure, such as quantum well type semiconducting lasers, high-electron-mobility transistors, heterobipolar transistors, resonant tunnel elements, superlattice elements, and the like. In most cases, the above-mentioned formation of single-crystal superthin film relates to heteroepitaxial growth of a semiconducting material on another semiconducting material. On the other hand, examples of heteroepitaxial growth of metal, e.g., superconductive metal, or insulating material, on a semiconducting material are rather rare.
The reason for it is in that the clean surface of most solid material has severed couplers (to be referred to as "dangling bonds", hereinafter). When one tries to grow a different material thereon, unless crystal structures or lattice constants are matched, not all such dangling bonds can be coupled, and the material growing thereon cannot become a single crystal. Thus, good heteroepitaxial growth is possible only between limited number of combinations of materials, in each of such combinations the materials having similar crystal structures and satisfying lattice matching conditions.
Even if the lattice matching conditions are satisfied at a high temperature for the heteroepitaxial growth, the two materials forming the heterostructure often have different coefficients of thermal expansion, and the lattice constants of such two materials become different, so that stress is introduced between the two materials as the heterostructure is cooled to room temperature.